A wiring unit is provided for robots having a rotary joint. This unit includes a wiring case, a slide aid contained in the wiring case, and a flexible printed wiring board for electric wiring. The wiring case includes a cylindrical housing and a reel with a cylindrical core member. The reel is relatively rotatable to the housing. The reel and housing are linked with robot's two members requiring the rotary joint. In the slide aid, an annular rotary plate surrounds the core member and is rotatable about the core member. Plural rollers are provided on the rotary plate and self-rotatable. The wiring board has electrical wires and is connected to the core member and housing and is wound and unwound in radially inside and outside spaces of the rollers via the vacant space by moving on and along the rollers.